This invention relates to an antenna for transmission/reception of radio frequency waves composed of a removable exciting element integrated into a fixed or mobile structure, for example an aircraft, making all or part of the structural element in which it is integrated radiate, and an aircraft using such an antenna.
In the remainder of the description, the antenna according to the invention integrated into the aircraft structure is considered as a non-limitative example. But it could also be integrated into any other type of vehicle.
An antenna has to be used in order to make a radio frequency link for transmission or reception. A dipole type antenna which is used particularly for radio frequency reception onboard an aircraft requires a ground plane with a large area and a sufficiently long antenna for the radio frequencies considered.
In an aircraft, the antennas are protected; the radiating part is sheltered by a radome composed partly of a material that is transparent to electromagnetic waves. This protection must be profiled so as to minimize disturbance to aerodynamic performances. Furthermore, electromagnetic decoupling values between the different antennas that must comply with the requirements of standards (particularly ARINC) result in physical separation constraints between antennas working in the same frequency bands.
Thus, in a small aircraft, the addition of an antenna can create problems.
In order to avoid disturbing the aerodynamic characteristics of an aircraft, it will be possible to use an antenna integrated into the structure of this aircraft.
An American patent U.S. Pat. No. 6,047,925 thus describes a narrow band UHF antenna integrated into the landing gear door of an aircraft. Due to its installation principle, the antenna has to be retuned after each time that it is disassembled. This action, if it has to be taken during a stopover of an aircraft operated by an airline company, is very inconvenient (extra cost, immobilization of the aircraft, very specialized tooling, etc.).
A French patent application FR 1 091 358 describes another type of antenna integrated into the structure of an aircraft. This antenna is a large band slit antenna, with relatively large dimensions. Therefore, it must form part of a structural element of the aircraft with appropriate dimensions (tail fin, etc.) without it being possible to separate the antenna from the structural element. Removing or replacing such an antenna requires disassembly and possibly replacement of the structural element considered. In addition to difficulties in installing such an antenna, maintenance costs are high and aircraft immobilization times are long.
The purpose of this invention is an antenna composed of an excitation element that can easily be integrated into a structural element forming the radiating part of the antenna without disturbing the overall aerodynamic performances, the said excitation element being removed from the structural element without needing to replace the structural element. In particular, the structural element may be part of a construction (for example a building or a ship) or a vehicle (for example an aircraft).
This invention divulges an antenna for the transmission/reception of radio frequency waves comprising:
a structural element that is conducting in the operating frequency band of the antenna, with size equal to at least one quarter of the wave length along the polarization direction of the electromagnetic wave for the minimum frequency of this frequency band, and comprising a cutout forming a cavity,
a removable exciting element placed in this cavity that acts as an exciter of this cavity,
a link that is electrically conducting at the operating frequencies of the antenna, providing metallization between the said exciting element and the said structural element.
In one advantageous embodiment, this exciting element comprises:
an element made of a material transparent to radio frequency waves filled with a material that is also transparent to radio frequency waves,
a conducting strip forming a stub, used for tuning and matching the antenna on the operating frequency band,
a cover made of a material transparent to radio frequency waves, containing the exciting element and maintaining continuity of the profile of the structural element,
a stub power supply line.
In one advantageous example embodiment, the exciting element and the cover are made of glass fiber. The material that fills in the exciting element is a resin or a cast thermoplastic material. The stub is made of copper covered on the surface with a silver plated layer. The cover is fixed to the exciting element using non-magnetic screws. The shape of the exciting element is such that it can be fixed in a notch formed in a structural element of a building or a vehicle, for example an aircraft.
This invention also relates to an aircraft in which at least one of the wing end elements comprises a notch-shaped cavity in which an exciting element like that described above is placed.
The antenna according to the invention has many advantages:
it does not modify the aerodynamic properties of the aircraft since it is integrated into a structural element of the aircraft,
it is easy to put into place and to maintain (disassembly, standard replacement, etc.); no adjustment or tuning operation is necessary after the antenna has been installed,
therefore maintenance costs are low,
it may be offered as optional equipment in an aircraft; it does not form part of the structure of the aircraft, but it can be fixed to the structure. A simple protective cover can thus protect the notch formed in the structure of the aircraft at the position at which the exciting element is fitted,
it may be integrated into a structural element sufficiently far away from other antennas using the same frequency band; this means that electromagnetic decoupling values imposed between antennas can be respected.